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Some background: I asked a longer version of this question here.

I recently bought a late 70s, two story home. I am working on (i.e. planning and budgeting) a project to wire the home for ethernet, wifi, poe security cameras, and other similar networked appliances.

As the home is two stories, I am lucky to have one wall that goes continuously from the bottom floor to the attic. Even better, there are closets on the other side of that wall.

So my hope is that it is possible and straightforward to relatively neatly tear out dry wall in these closets and install metal conduit to use as a raceway.

But what does a craftsmanlike installation look like?

I know that I will be drilling through the floor, top plate, and fire blocking in the wall, and that I'll have to put in my own fire blocking at each penetration.

My questions:

  1. What kind of conduit should I use? I like the sound of plain 1.5 or 2 inch flexible steel or aluminum conduit, and maybe installing two. But there us a minor complication, since the crawl space is a plenum space, and I don't know if that means anything for the conduit.

(I specifically like the idea of flexible conduit because I am still unsure what exactly is in that wall, and the flexibility would help me get around small obstructions in the run)

  1. Relatedly (because of the plenum space possibly affecting the conduit I need), I don't necessarily want a whole lot of conduit installed in the plenum crawl space beyond what is necessary for the riser. Although I am unsure how the installation will look in the crawl space (still planning it all out), I am open to having very little conduit down there (i.e., just enough to attach it securely and fire stop it) or having a full run from the riser to my server room.

Heck, I can even give some background into question 2. I was looking into flexible metal conduit, and it appears that I can get some very high grades liquid tight FMC that would appear to work in a plenum space, but are extremely expensive. (So if I can get away with just having 6 to 8 inches of lower/normal grade PVC FMC in the plenum space and that's good enough for code, I'm okay with that. Or we can attach it to solid conduit and continue the run. Etc).

In the most ideal case, I'd be able to run a cable from my attic into the server closet's wall with a single long fish tape or similar. That's probably about 50 feet of conduit, and 180 degrees worth of turns. I'm not sure if that's feasible either. But it's a goal and it would eliminate some options.

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  • Bending 1-1/2" or 2" EMT by hand is not for the light of weight (I think 1-1/4" is about as big as you are going to get with a hand bender) - some supply houses will bend it for you, though. Flex will most likely require additional support, so it would help to know how the studs line up and what else is in the wall.
    – red_menace
    Nov 3, 2021 at 21:47

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Do not choose liquidtight if you want FMC. So far the single most obnoxious type of conduit I've ever pulled through. Also outrageously expensive. Does it rain inside your house?

If you insist on flex, get the stuff that looks just like empty armored cable (which is the type: FMC conduit, not surprisingly) - a long coiled strip of steel (or aluminum), interlocking to make a tube, helically. No plastic coatings to burn or make your cables want to stick.

It's just galvanized steel, (or aluminum) nothing to burn, fine in plenum spaces. Alternatively, get plenum-rated smurf-tube flexible plastic conduit (ENT.) Not surprisingly you'll find vast amounts of that in data centers - it works.

If your cables stay inside the conduit in the plenum space, nothing special needed, and you might be able to do the simple pull. If you run your cables outside of conduit in the plenum space, then you need plenum-rated cables (every last one.) The bare minimum to do a "workmanlike" exit from conduit for data cables is to put a "bell end" fitting on that prevents cutting or sharply bending the cables on the edge of the conduit.

I would strongly recommend running EMT (steel) non-flexible conduit through the crawlspace as it keeps the cables contained and does not flex. A problem with flex is that every bend in flex adds to your bending limit - so the 180 degrees you think you have becomes actually much more, because flex does not run straight (say across the crawlspace) unless something constrains it to be perfectly straight - so it wiggles side to side, or droops between joist attachment points, and you have an extra 90 degrees of bending (5 or 10 degrees at a time, repeated) you didn't count. Flex can be used just at the points where things can't be straight, if you don't want to deal with bending, as one approach.

As a practical and cost note, unless you are running terminated cables through and need a big hole to do that, it's easier to run multiple 3/4" or 1" conduits in parallel than a single giant tube which takes you out of the range where common hand tools work for bending, etc.

Another practical note is that if you use a fish tape at all (I rarely do) you use it once. Fish tapes can do serious damage to cables when jammed into an occupied conduit. Every time you pull in cables, you pull in a new piece of "pull string" (aka "JetLine" which might be brand name) or "pulling tape" so you can pull the next cable in. Usually I get that in with a vacuum cleaner, not a fish tape. If you are pulling 10 cables, better to pull all 10 at once, not one at a time.

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  • My experience has been that jet line can cause a lot more damage, especially around bends. You can even use it to saw through PVC raceway.
    – red_menace
    Nov 4, 2021 at 15:28

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